On Monday, China’s top COVID-19 health official announced that China plans to vaccinate 40% of its 1.4 billion people by the end of June. The announcement marks China’s first publicly stated vaccine target and will require a significant ramp up in China’s distribution of doses since its vaccine campaign currently lags behind similar rollouts in places like the U.S. and the U.K.

Zhong Nanshan, an epidemiologist and head of the COVID-19 expert group at the China National Health Commission, laid out the ambitious target at a Monday panel convened by U.S. think tank the Brookings Institution and Tsinghua University. On Tuesday, Zhong clarified to Reuters that China was more likely to achieve its 40% target by the end of July, after taking into account people who will reject the vaccines.

Whether it’s by June or July, the 40% goal will require China to deliver doses to some 560 million people in the next several months and dramatically scale up its current distribution efforts.

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As of Feb. 28, China had administered 52 million COVID-19 vaccine doses, which translates to roughly 3.56 doses per 100 people, Zhong said on the call. The U.S., by contrast, has administered nearly 77 million vaccine doses, translating to just over 23 doses per 100 people. Israel, meanwhile, has administered just over 8 million vaccine doses, which equals roughly 90 doses per 100 people.

Chinese officials attribute China’s relatively slow rollout to the country’s relative success in containing COVID-19 within its borders.

“The current vaccination pace is very low today due to the outbreak control in the early stages,” Zhang Wenhong, another infectious disease expert and COVID-19 government adviser, told the panel on Monday.

Chinese authorities have officially approved four Chinese vaccines to be part of its campaign.

In January and February, regulators approved COVID-19 vaccines from state-owned maker Sinopharm and the private firm Sinovac for general distribution. Last week, China added two more vaccines to its arsenal—one from the Wuhan Institute of Biological Products, a Sinopharm affiliate, and another from CanSino Biologics, a private vaccine maker that has partnered with China’s military to produce its vaccine.

With the four vaccines, Zhang said that he’s confident China’s supply could meet the 40% target: “[China’s] vaccine capacity…is very high and is expected to increase to 2.1 billion doses by end of 2021.”

CanSino’s vaccine, in particular, is raising hopes that China can dramatically accelerate its immunization campaign. Based on technology similar to that of Johnson & Johnson’s shot, CanSino’s vaccine requires only one jab to provide protection. The other three vaccines at China’s disposal require two doses.

Last week, a military researcher working on CanSino’s vaccine told Chinese media that CanSino is currently on pace to produce 500 million doses of the vaccine per year but didn’t clarify if that many doses could be manufactured in 2021.

China’s domestic vaccination efforts may also be slowed by lingering questions over the effectiveness of its homegrown inoculations. The manufacturers have reported efficacy rates ranging from 50% to 90% effective, but none have published Phase III trial data in peer-reviewed journals—medicine’s gold standard—to back up their claims.

It is also unclear how China’s effort to export doses to other countries is interfering with its vaccine campaign at home. China has pledged to send roughly half a billion doses to 45 countries, according to the Associated Press.

As of mid-February, China reportedly shipped over 46 million doses of Chinese-made vaccines abroad, nearly matching the figure Zhong said China had administered domestically.